About OSS degrading image quality

I would tend to agree with your sentiment, but I talked to someone a few days ago who is absolutely convinced that using filters will save his lenses. He told me how he banged/dropped the camera and only the filter was damaged, and how he's paranoid about cleaning the front lens/element. Also, some famous photographer supposedly recommends it.

Personally, I've never ruined a camera or lens by dropping it and having it land exactly lens-down, so this feels like paying extra for "insurance"; it's not cheap to put a "good" coated filter on each lens. I've seen (online) demonstrations of how flare can be worse wih filters, and decided it's not worth the hassle and expense and the potential loss in IQ, but I'm sure there are the cases where it does save someone's lens from damage. I also try not to buy expensive lenses, then I don't lose sleep about possibly breaking it..

High quality filters have surface treatments that make them much more resistance to scratching than the front element glass of a lens. The front element of wide angle lenses especially seem bulbous and exposed and since those lenses also happen to be the ones that benefit most from a polarizer, it all works out anyway.

Having said that, I did put a UV filter on my 70-200 for indoor use. I don't know if it ever helped prevent scratches, but it just seemed like that huge lens was prone to bumping into things in a crowded wedding situation and I wanted it covered. And now that I'll be selling it, it's nice that it's in mint condition. But that was a special case. I generally never buy UV filters due to issues with ghosting and flare outdoors.